classes connection

I downloaded project from
Can anyone explain, how does it run, if my classes are not connected to each other ?
i mean in both classes i cannot see any mentions of other class

Sounds like your first application. You should really read up about the used software - here for example spring boot as underlying container that handles Inversion of Control, Dependency Injection and other stuff so you don’t have wire anything manually.

i could not find explanation

In the background Vaadin takes care to registry the routes they have found by scanning your app.

Thank you